In Non-Patent Literatures 1 and 2, a technique referred to as OpenFlow has been proposed. OpenFlow recognizes communications as end-to-end flows and performs path control, failure recovery, load balancing, and optimization on a per-flow basis. Each OpenFlow switch according to Non-Patent Literature 2 has a secure channel for communication with an OpenFlow controller and operates according to a flow table suitably added or rewritten by the OpenFlow controller. In the flow table, a set of the following three is defined for each flow: Match conditions (Match Fields) against which a packet header is matched; Flow statistical information (Counters); and Actions that define at least one processing content (see section “3 Flow Table” in Non-Patent Literature 2).
For example, when an OpenFlow switch receives a packet, the OpenFlow switch searches the flow table for an entry having a match condition that matches header information of the received packet (see “3.4 “Matching” in Non-Patent Literature 2). If, as a result of the search, the OpenFlow switch finds an entry that matches the received packet, the OpenFlow switch updates the flow statistical information (Counters) and processes the received packet on the basis of a processing content(s) (packet transmission from a specified port, flooding, dropping, etc.) written in the Actions field of the entry. If, as a result of the search, the OpenFlow switch does not find an entry that matches the received packet, the OpenFlow switch transmits an entry setting request to the OpenFlow controller via the secure channel. Namely, the OpenFlow switch requests the OpenFlow controller to transmit control information for processing the received packet (Packet-In message). The OpenFlow switch receives a flow entry from the OpenFlow controller and updates the flow table. In this way, by using an entry stored in the flow table as control information, the OpenFlow switch performs packet forwarding.
Patent Literature 1 discloses a path information management apparatus used for an autonomous-distributed-type network such as a TCP/IP (Transmission Control Protocol/Internet Protocol) network. More specifically, the path information management apparatus includes a path information reception unit for receiving path information representing change of a communication path and path information indicating cancellation of a communication path from a communication path observation apparatus. In addition, the path information management apparatus includes a path state table creation unit for creating a path state table in which a path presence period on the basis of the reception time of path information and a range of an address space represented by values obtained from prefixes included in the path information are stored for each communication path. The path state table creation unit stores these path state tables in a path information database.    Patent Literature 1: Japanese Patent Kokai Publication No. 2008-288848A    Non-Patent Literature 1: Nick. McKeown, and seven others, “OpenFlow: Enabling Innovation in Campus Networks,” [online], [searched on Dec. 26, 2012].    Non-Patent Literature 2: “OpenFlow Switch Specification” Version 1.0.0 (Wire Protocol 0x01), [online], [searched on Dec. 26, 2012].